Conventionally, as a material useful for a high-frequency band device, Ba(Mg1/3Ta2/3)O3 materials have been known. Although the Ba(Mg1/3Ta2/3)O3 materials have a very high Qf value, they are materials difficult to be sintered. That is, it is necessary to be sintered for a long time in accordance with a rapid temperature-up sintering process or a sintering process in oxygen, for instance, at a temperature-up speed in the range of 500 to 1000° C./min, at a sintering temperature in the range of 1500 to 1600° C. for a sintering period of substantially 100 hr, resulting in lacking the mass productivity and in difficulty of obtaining stable Qf value.
Furthermore, in order to use them in a high-frequency band device, the temperature coefficient τf at a prescribed resonant frequency has to be controlled depending on the applications. However, Ba(Mg1/3Ta2/3)O3 materials are known to have τf in the proximity of +1.5 ppm/° C. and it is difficult to control the τf thereof because they are made of a single compound.
As a material that can be improved in sinterability and can be controlled in temperature coefficient τf, a composition having a composition formula represented by XBa(Mg1/3Ta2/3)O3—Y(BazSr1-z)(Ga1/2Ta1/2)O3 has been proposed (see, patent document 1). Although this composition has a high Qf value (250,000 GHz or more) and is controllable in temperature coefficient τf, there still remains a problem in sinterability and, since the temperature coefficient τf at a resonant frequency is substantially in the range of 3 to 4 ppm/° C., it is difficult to control it to the proximity of zero.
On the other hand, as a composition that can be controlled in temperature coefficient τf at the resonant frequency, a composition represented by XBa(Zn1/3Ta2/3)O3—Y(BazSr1-z)(Ga1/2Ta1/2)O3 has been proposed (see, patent document 2). Although this composition is controllable in the temperature coefficient τf, there is a problem in that, in comparison with the composition shown in the patent document 1, the Qf value is low to thereby result in restriction on use in a high frequency region of 10 GHz or more.
In this connection, the present applicant has proposed, as a composition that maintains a high Qf value to enable control of the temperature characteristics τf and shortening of the sintering period, a composition represented by XBa[(Mg1-zZnz)1/3Ta2/3]O3—YSr(Ga1/2Ta1/2)O3 (see, patent document 3).                Patent document 1: JP-A-4-260656        Patent document 2: JP-A-11-189468        Patent document 3: JP-A-2003-226575        